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RFC 1519

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Network Working Group
Request for Comments: 1519
Obsoletes: 1338
Category: Standards Track

V. Fuller
BARRNet
T. Li
cisco
J. Yu
MERIT
K. Varadhan
OARnet
September 1993

### Classless Inter-Domain Routing (CIDR):
an Address Assignment and Aggregation Strategy

### Status of this Memo

This RFC specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.

### Abstract

This memo discusses strategies for address assignment of the existing IP address space with a view to conserve the address space and stem the explosive growth of routing tables in default-route-free routers.

### Table of Contents

1. Problem, Goal, and Motivation
2. CIDR address allocation

2.1 Aggregation and its limitations
2.2 Distributed allocation of address space

3. Cost-benefit analysis

3.1 Present Allocation Figures
3.2 Historic growth rates
3.3 Detailed Analysis

3.3.1 Benefits of the new addressing plan
3.3.2 Growth rate projections

4. Changes to inter-domain routing protocols and practices

4.1 Protocol-independent semantic changes
4.2. Rules for route advertisement
4.3. How the rules work
4.4. Responsibility for and configuration of aggregation
4.5 Intra-domain protocol considerations

5. Example of new allocation and routing

5.1 Address allocation
5.2 Routing advertisements

6. Extending CIDR to class A addresses
7. Domain Service considerations

7.1 Procedural changes for class-C supernets
7.2 Procedural changes for class-A subnetting

8. Transitioning to a long term solution
9. Conclusions
10. Recommendations
11. References
12. Security Considerations
13. Authors' Addresses

Original text document

### Acknowledgements

The authors wish to express their appreciation to the members of the ROAD group with whom many of the ideas contained in this document were inspired and developed.

Next: 1. Problem, Goal, and Motivation

Connected: An Internet Encyclopedia
RFC 1519